The Acoustic Response of Some Gas-Charged Sediments in the Northern Adriatic Sea

Abstract

High-resolution profiles obtained in the northern Adriatic Sea with a Uniboom (EG&G) sub-bottom profiling system revealed peculiar acoustic features down to a depth of about 70 m below the sediment surface. Several different structures due to high gas contents are described and explained for the first time in the northern Adriatic. They range from the so-called “basin effect” and cone-like structures to acoustic voids. Gas seeping from the bottom has also been observed. The abrupt disappearance of acoustically significant horizons is discussed, and a tentative explanation is given. Possible migration of gases and trapping effect are also discussed. The importance of high--quality, high-resolution recording is stressed in order to detect the anomalies — due to gases — in the sea floor, and to evaluate their potential as geologic hazards for offshore installations.